The site can not be cached by Dreamhost because there is a motopress cookie which breaks the caching (dreamhost). The support from Dreamhost says :
“The motopress-hotel-booking plugin is putting cookies down on every single page, this causes each session to be unique and breaks the server cache. You would want to reach out to the plugin developers to see if they can offer any suggestions to make the plugin cache friendly via current settings or push an update to the plugin that fixes it.”
Thanks for the interesting question. I have contacted our developers and they ensured me that no plugin cookies could cause server cache to not function. I would recommend that you consult with DreamHost about other possible reasons causing server caching issue, since it is not likely the plugin that does it. If you/they have any further concerns, you may submit your request to our Help Desk.